It is our long term goal to elucidate the structural details of how peptides interact as substrates for transport or as transmitters of information with their receptors in biological membranes. Our objectives for the present proposal are to identify membrane proteins responsible for a particular peptide receptor function and to probe the quarternary stucture of that receptor. To this end, three model systems will be investigated: Peptide transport systems in E. coli will be probed with endo photoaffinity reagents in which an aromatic residue is replaced with a (4-azido-2-nitro)-L-phenylalanyl residue, in an attempt to identify structures involved in transport. The extracytoplasmic surface of the membranes of photoaffinity labeled cells will be reacted with membrane impermeable cleavable crosslinking reagents, such as diisethionyl-3,3'-dithiobis(propionimidate), in an effort to determine whether the receptor is an oligomeric structure and whether it is physically coupled with other functionally identifiable structures in the membrane. This techique will be used in an attempt to identify the E. coli secretory receptor, i.e., the membrane structure which recognizes the initial sequence of the nascent chains of secreted proteins and mediates the transport of the growing polypeptide chains through the membrane. We will also use cleavable crosslinking techniques in an attempt to identify the receptor for the mitogenic and gastric antisecretory hormone epidermal growth factor, in the plasma membrane of A-431 cells.